No one would be surprised to learn that kids suffer when their parents argue. Still, detailed research on exactly how kids are affected and which aspects of parental conflict are most harmful can help families and communities to address the problem effectively. Parental Conflict: Outcomes and interventions for children and families, a short volume from the UK think tank One Plus One coauthored by four researchers, offers an accessible but detailed overview of scholars' findings on these subjects. Here are some highlights of the research they present.

Which aspects of parental conflict matter?

There is no such thing as a relationship entirely free from conflict and disagreement, and surely all children see their parents argue at one time or another. When parents relate to each other calmly and positively even during a disagreement, solve the problem together, and show children through their subsequent interactions that the conflict has been resolved, then the children may be unaffected (and a small body of research suggests they may even learn conflict-resolution skills, which they can apply to their own relationships down the road, from such situations).

Parental conflict is harmful to kids, however, when it is frequent; when it is heated and hostile, involving verbal insults and raised voices; when parents become physically aggressive; when parents withdraw from an argument or give each other the silent treatment; when the conflict seems to threaten the intactness of the family; and when it's about the child. (The impact of witnessing domestic violence on kids is not explored in detail in this book, but of course it too has been shown to be very harmful.) And conflict is harmful regardless of whether parents are married or even living together.

How exactly do children suffer from their parents' conflicts?

From a very early age—as young as six months, some researchers say—children show distress when their parents fight. Their reactions can include fear, anger, anxiety, and sadness, and they are at higher risk of experiencing a variety of health problems, disturbed sleep, and difficulty in focusing and succeeding at school. They may "externalize" their distress in the form of "aggression, hostility, anti-social and non-compliant behaviour, delinquency and vandalism," or "internalize" it in the form of "depression, anxiety, withdrawal and dysphoria."

In addition, "children from high-conflict homes are more likely to have poor interpersonal skills, problem solving abilities and social competence." Those problems negatively impact their romantic relationships in adolescence and adulthood, as conflicts cause children to "perceive themselves and their social worlds more negatively" and to "have more negative pictures or internal representations of family relationships." Thus the high-conflict relationship of one couple can produce other negative relationships in the next generation.

Why does parental conflict produce these effects?

Conflict between parents harms kids in part because of a spillover effect: parents in high-conflict relationships tend to be worse parents, engaging in more criticism, aggression, making threats, shouting, and hitting. High-conflict relationships can also produce lax and inconsistent parenting: parents who simply don't pay much attention to their children. In either case, children may fail to form a secure attachment to parents as a result.

But parental conflict also seems to harm kids even apart from its effects on parenting. Researchers have proposed a variety of frameworks and mechanisms that may explain this process. To give one example, in the struggle to understand their parents' conflict, children can come to blame themselves or find harmful ways of coping with the conflict. In addition, on top of their negative emotions, children experience physiological reactions related to stress that may harm their brain development.

Why do the effects of parental conflict affect some children differently from others?

A large number of variables shape the impact of parental conflict: the age, sex, and temperament of the child; the child's coping strategies; and the child's physiological reaction to stress. Family characteristics matter, too: sibling relationships, attachment to parents, parents' mental health and substance use, and socioeconomic pressure all affect how children react to conflict.

While socioeconomic pressure tends to worsen parents' mental health and increase parental conflict, the link between conflict and child outcomes remains significant when socioeconomic pressure is accounted for. (In other words, "children are vulnerable to the impact of a high conflict home regardless of their parents' socioeconomic situations.") Moreover, although genes could matter for some aspects of parental conflict and children's reactions---for example, shaping children's temperaments, mental health, and physiological reactions to stress---some studies suggest that parental conflict is associated with negative child outcomes even for adopted children, who are genetically unrelated to their parents.

More details about (and citations for) all the topics I've mentioned here can be found in the book. In a subsequent post I'll outline the researchers' findings about preventing couple conflict and intervening in high-conflict relationships.